From my experience, you can win up to 0.01 BTC with 0.001 deposited on a new gambling site during a promotion. Only you shouldn't be too greedy thinking "What if I deposit 0.1? I can win 1 Bitcoin then!". Remember, dealing with newly appeared gambling sites is still very risky, and you might never see your deposited money again. And not because you can lose them to a game, but because you wouldn't be able to withdraw your balance from that site.